Electric insulation board and method of making same



Patented Aug. 24, 1926.

UNITED STATES ELECTRIC INSULATION BOARD AND METHOD OF MAKING SAME.

' Io Drawing.

M invention has reference to electricinsu ation boards and bodies, andis in the nature of an improvement upon or a carrying forward of thatset forth and claimed in an application filed in my name on the 6th day'of November, 1923, and designated by Serial Number 673,221 which becamePatent 1,554,895.

Underrthis as under the prior invention, a board, sheet or body isformed of pulp or cellulose, combined with-gilsonite, asphaltum, mineralpitch, elaterite, resin, or other usual binder, which board or body isdried to a suitable degree, and is then given a thin coating of somesubstance which will prevent the board or body from adhering to thecontacting surfaces of a press or mold in which it is subjected to finalcompression in the presence of heat. vent adherence to other sheets orsurfaces after completion, such coating combining with the bodyof thesheet or board under the final pressure and heat, and ensuring a smooth,'firm surface, devoid of tackiness and capable of being buffed,sandpapered, or otherwise finished after the manner of finishingotherhard surfaces.

Under the procedure of the prior invention, cellulose acetate varnish orlacquer was used for such coating, and with very satis-' factory resultsin the main; but cellulose acetate is relatively expensive and addsmaterially to the cost of the product, and though producing a quite goodsurface, does not give the best obtainable results in that regard, ordoes not produce the kind of surface generally deemed most desirable forsuch insulating boards or bodies. I have found that a. varnish orlacquer of acaroid-resin dissolved in alcohol, in the proportion ofabout two pounds of resin to one allon of alcohol may be used in lieu oft e cellulose acetate varnish or lacquer, with excellent results as tothe final product, and at materially lower cost. The present inventionhence resides in the use or employment of such acaroid resin varnish orlacquer in the place of a varnish or lacquer of cellulose acetate, inthe rocess of manufacture of insulation board; or bodies.

Better to identify the resin employed and above referred to as acaroidresin. it may be stated that it is also or commercial names: GumAcroides, Red

Acaroid Resin, Yacca Gum, and Grass Tree It also serves to preknown bythe trade" Application filed August 4, 1924. Serial No. 730,022.

Gum. Its botanical names are: Kan-thorrlzoea australz's, Xantiwrrhoeaquadrangu- Zaris, anthom'hoea drumflwndz'i, and Xanthorrh'oea prez'sz'i.There is also another grade of acaroid resin known as Xantlzorrhoeakastz'lz's, and quite commonly called Botany Bay Gum. It is likewisesometimes known as Black-boy Gum. 'lVhile there are slight variations'inor differences between certain of-the gums known under the several namesabove given, they are essentially alike in character and properties, andall are found serviceable as a coating for thesheet, slab or body afterformation and partial drying.

The process of manufacture of the improved board may be briefiy'statedas follows:

A pulp composition consisting essentially of cellulose of usualcharacter combined with a suitable binder as mineral pitch, elaterite,resin, or other, is formed into a sheet, slab or body in any common'andwell-known way, and 'a large percentage of the liquid or moisture isthen removed therefrom, preferably through pressure applied in a mold orpress of suitable form or construction.

I Preparatory to the final compression necessary to secure the requisitedensity, there is,applied to the sheet, slab or body by dipping,spraying, brushing, or otherwise, a thin coating or layer of varnish orlacquer composed of acaroid resin dissolved in alcohol or other knownsuitable solvent thereof, in the proportion of ap roximately two (2)pounds of resin to one 1) gallon of alcohol.

The alcohol may be denatured thoughthis is not necessary. The amount ofresin used in the varnish or lacquer should not materially exceed twopounds per gallon of solvent, as stickiness is likely to result, and itis further apt to cause a brittleness of the film or coating and acracking or crazing thereof.

The sheet, slab or body having been thus coated on its several faces, oron any face or faces desired, is next subjected to heavy compression,preferably in a hydraulic press, and at the same time subjected to heat.For this purpose it is customary to employ presses having a hollow bed,hollow platen, or both, and to supply the chambered memberor memberswith steam or other heating medium. After compression as reached thegilsonite, asphaltum,

proper point or degree, and as been con tinned for a time sufiicienttogivethe required density and set the sheet, slab or body permanently,the temperature is lowered,

and the body treated isccooled. This gradual cooling serves to preventcracking, checking or crazing of the finished surface, and leaves itsmooth and unbroken throughout. Under the pressure andheat the var- Inish or lacquer coating enters into and unites or combines withthe-cellulose body, and be- I comes an integral part thereof.

Any desired color may be imparted to the varnishor lacquer prior to itsapplication toY-thesh'eet, slab or body, by incorporating therein andthoroughly distributing through the same, a suitable pigment orpigments.

If it be desired to render the sheet, slab or body more or less pliableor flexible, a suitable softening agent or agents such as methyl esterof paratoluelsulphoneamide, triphenyl phosphate, triacetin, or the like,may be added to the varnish or lacquer employed. Care should be taken toavoid excess of such agent, since an undue quantity begets efliorescenceon the surface of the product.

Except as herein described theprocess may be the same as that set forthin my application above mentioned, with the single highly polishedsurface, a flat finish, or what is commonly termed an egg shell finish.

The di-electric properties of the'finished product are in no manner ordegree impaired through the utilization of the varnish or lacquer havingthe acaroid resin base, and said roduct may be safely used as a panelboard or base for electrical appliances requiring a high degree ofelectric insulation. It can be drilled, cut, and machined with thefacility of and in practically the same manner as indurated fiber, hardrubber, and other like bodies.

The foregoing sets forth the preferred mode of procedure, but theacaroid; resin may be incorporated in the cellulose or pulp compositionby dissolving it in caustic soda and precipitating it with alum inconjunction with gum resin, oil soaps, asphalt, and other well-knownbinders, but 'in all, other respects the rocedure will be as first abovedescribed. oatin with the lacquer or varnish as .contradistmguished fromincorporating the acaroid resin in the pulp mass is, however, the.preferred procedure.

What is claimed is 1 The herein described method of producing anelectro-insulation sheet, slab or body, which consists in forming thesame of a pulp composed of cellulose and a suitable binder; removing alarge percentage of the liquid or moisture contents therefrom; coatingthe same on its exterior with a lacquer or varnish of acaroid resindissolved in alcohol; subjecting said body'to high compression in thepresence of heat and maintaining such pressure and heat until theacaroid resin combines with the binder of the cellulose body and thebody becomes dense and set; and finally cooling the same while stillunder pressure.

2. As a step in the manufacture of electrio-insulation boards or bodies,the application to the surface thereof and prior to complete drying ofthe board or body, ofa lacquer or varnish consisting of acaroid resinand a suitable solvent, preparatory to final compression in the presenceof heat, the resin so supplied serving to prevent adhesion of thefinished product to the surfaces of the mold or press in which suchfinal compression takes place, or to bodies with which it maysubsequently come into contact.

3. The method of finishing electric-insulation sheets, boards and bodiesformed of pulp composed of cellulose and a suitable binder, whichconsists in incorporating in the surfacethereof after the same is'shapedand deprived of the bulk' of its moisture content, acaroid resin;subjecting the body so prepared to heavy compression in the presence ofheat; and finally cooling the body while still held under com ression.

4. As a new article of manu acture, an electric-insulation sheet, boardor body having a smooth even surface produced by incorporating thereinand uniting or combining therewith, acaroid resin.

5..As a new article of manufacture, an

electric-insulation sheet, board or body hav-- ing a surface impregnatedwith acaroid resin united or combined with the cellulose base and itsbinder through high compression in the presence of heat.

6. As a new article of manufacture, an electric-insulation board, sheetor body composed of cellulose and a binder such as described, and havingits surface impregnated .with acaroid resin, combined with said binderand deprived of stickiness or tackiness through compression and heat.

7. An electric-insulation sheet, slab, or body formed of cellulose and asuitable binder, and having acaroid resin incorporated and bound in itssurface.

In testimony whereof I have signed my f

